Where that finish line is located is anybody’s guess, because the reserved Luck isn’t telling anybody as he appears to be getting closer to the final stages of returning from January's right-shoulder surgery.

"There has been an effort not to skip steps," he said last week. "I think we're progressing along with the plan nicely, and it would be foolish to get close to the finish line and start skipping steps."

But the timetable for his return has been fluid since January. Here's a look at how we got here, to the brink of the much-anticipated return of Luck.

How did Luck injure the shoulder?

Not many people thought that six weeks into the regular season the quarterback would still be on the sideline, watching as a spectator in a Colts T-shirt and hat. Owner Jim Irsay tweeted on Jan. 19 that Luck would be ready for the start of the regular season.

Andrew recovering from successful outpatient surgery to fix right shoulder injury that had lingered since 2015. Will be ready for season!

It was more than two years ago, on the same field where Luck and the Colts will be playing the Tennessee Titans on Monday night, that the quarterback originally injured his shoulder.

Nobody knew the severity of Luck’s right shoulder injury at the time because he finished that game on Sept. 27, 2015. He even threw two touchdowns 56 seconds apart in the fourth quarter in the Colts' come-from-behind victory.

“I did not know it was his shoulder; I thought it was just his sternum or rib-related because of when I tapped him like that in the video that everybody saw afterward,” former Colts quarterback Matt Hasselbeck said. “I didn’t know, or I wouldn’t have done it. In that game, we were 0-2, and he brought us back, seriously, by himself. Throws the game winner; it was a heck of a throw. Basically it was like, ‘If you can make that throw, you’re fine.’ I did believe he was fine. I didn’t think it was an issue.”

How did he reinjure the shoulder?

Luck missed the following two games with a right-shoulder injury. He returned to play four games before his 2015 season ended due to a lacerated kidney suffered against Denver in Week 9.

Luck reaggravated his right shoulder while trying to tackle Denver cornerback Aqib Talib after throwing an interception that was returned for a touchdown in Week 2 of the 2016 season. Irsay said less than two weeks later that Luck wouldn’t need surgery on the shoulder.

Andrew Luck re-aggravated his right shoulder while trying to tackle Aqib Talib after throwing an interception early last season. Justin Edmonds/Getty Images

“Look, [Luck] throws the interception, he’s mad, I know,” Irsay said the day before their Week 4 game in London. “Do what Peyton [Manning] did. Do a little foxtrot, and you don’t embarrass yourself. But you stay out of the fray. You don’t see Aaron Rodgers [do it]. You don’t see quarterbacks get involved in those types of frays. That’s when tough things happen.”

Luck, who played every meaningful snap during his first three seasons, spent at least one day a week on the team’s injury report due to his shoulder last season. Oftentimes, Luck wouldn’t throw during the portion of practice that was open to the media. He often spent that time handing the ball off to the running backs while Scott Tolzien and Stephen Morris threw passes.

But despite the limited practice time, Luck didn’t let his shoulder hinder him completely. He threw for 4,240 yards and 31 touchdowns while completing a career-high 63.5 percent of his passes in 15 games last season.

When did the Colts realize the injury was still an issue?

The severity of Luck’s shoulder problems came to light when the surgery was announced nearly three weeks after the Colts finished their second straight 8-8 season. It was also determined then that he wouldn't take part in the team's offseason activities.

Irsay, as he mentioned the day the team announced Luck’s surgery, told reporters during the owners meetings in Phoenix that the quarterback would be ready for the start of the regular season despite knowing that he would miss all of the team’s offseason workouts.

“We are not going to be rushing him," Irsay told Colts.com in Phoenix in March. “We are going to make sure, obviously, that the shoulder has to be ready, and the doctors are going to give full approval before he starts putting real reps on it. This is going to be a real benefit in the long run. We really feel that he’s going to be completely healed for the season and he’s going to have a great season."

Andrew Luck has been on the sideline for all of the Colts' games this season. Joe Robbins/Getty Images

When did it become a possibility that he wouldn't be ready for camp?

It wasn’t until the NFL’s draft weekend at the end of April that there became a realistic possibility -- at least publicly -- that Luck wouldn’t be ready for the start of training camp. General manager Chris Ballard started what became a common saying by him and coach Chuck Pagano that the franchise was not going to rush Luck back because they’re more worried about his longevity than the short term.

Ballard, speaking less than a week before training camp in late July, said Luck had started throwing, but he would open camp on the physically unable to perform list with the intention being off of it at the start of the regular season.

"The endgame is for me to be better than I was before I got injured, and I don't want to put a date on that, in a sense," Luck said on July 29. "I think that's really sort of unfair. I know, when I'm playing, things are going to be weird for a sense. From guys I've talked to that have gone through shoulder injuries at this position, it's different and it takes a little time to sort of find the groove, if you will, and find the rhythm."

When did Luck return to practice?

Luck, after much anticipation and wondering, practiced, albeit on a limited basis, for the first time on Oct. 4, in shorts, a red, noncontact jersey and a helmet while the rest of his teammates were in full pads. He was the scout-team quarterback, running Tennessee’s offense, during 7-on-7 drills in practice on Oct. 11. It was just a short period after Luck said he was getting close to the finish line, more than two years after the original injury.

When will Luck play?

As long as he hasn't suffered any setbacks, Luck is expected to continue to increase his workload once the team returns to practice Wednesday. The Colts host the Jacksonville Jaguars at Lucas Oil Stadium on Sunday.

Playing Luck against the Jaguars means he'd be returning having barely more than two weeks of practice after his nine-month layoff. As talented as Luck is, that still may be too soon for his return. A Week 8 game at Cincinnati seems more ideal.